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What is jаvascript: purpose, features and scope of the language

04 December 2021, Saturday By Priyanka Boruah

Interactive elements of websites and mobile applications are often executed in jаvascript. It integrates well with HTML/CSS code and is supported by major browsers and is included by default. Therefore, no questions arise with the launch of web resources, they work without user intervention.

Let's take a look at what jаvascript is, what tasks it solves, and in what areas it is used. 

Jаvascript features

Jаvascript Tool (JS in short) is a high-level programming language that can be embedded in other applications. All types of functional modules are created as scripts. In syntax, it is similar to the Java language, but they share only part of the name. The platform is regularly updated, the code is becoming more rational.

Related: Levels of programming languages: a brief overview

What is JS

Features of the language:

  • JS was originally developed on the "write less, do more" principle.
  • The code supports functional, imperative, and event-driven styles.
  • The platform is distributed free of charge without royalties to developers.

Jаvascript syntax is not suitable for all tasks. This has led to the emergence of a number of artificial languages ​​that are transpiled (converted) after being run in a browser. Developers write code in a language they understand, and the platform converts it to JS on the fly. Examples: CoffeeScript, Flow, Dart, TypeScript, Brython.

Jаvascript Application Areas

Mastering the basics of jаvascript is useful for anyone involved in the development and promotion of websites. Any resource contains at least 3-4 scripts - from the Google Analytics counter to a contact capture form, social media widgets or account registration. The platform's popularity has an explanation: the language is safe, it does not provide low-level access to server processes.

JS Code

JS scripts are used in the following ways:

  • the client side of any web applications,
  • interactive elements of interfaces in AJAX,
  • mechanism for issuing push notifications based on the Comet model,
  • programs compatible with Android, iOS, Windows Mobile,
  • browser operating systems such as webOS,
  • macros for automating routine office operations,
  • applications running on servers C, C++, Java, Go.

We should also mention custom scripts in browsers. They implement such features as automatic filling of forms, formatting content on the page, hiding and reflecting content depending on the region. Extensions, plugins (widgets) for popular CMS like WordPress, MODX, 1C-Bitrix are written in a similar way.

What operations can JS perform

The use of jаvascript scripts is driven by the desire to add functions that are not and will not be in HTML/CSS. For example, processing the input of contacts (sending to the specified email, issuing messages, automatic callback). Due to its multi-paradigm nature, JS is capable of performing operations of various types.

What operations can JS perform


  1. Mathematical calculation - Scripts replace calculators for calculating the cost and volume of materials, and certain messages are generated as a result. For example, if the site contains tests, JS displays a description that matches the points scored.
  2. Processing and validation of data in HTML- forms - There are many use cases - from determining whether all fields are filled in to checking compliance with the specified format (numbers, letters, their combination). Such scripts are able to work without contacting the server.
  3. Interaction with the user - This includes drop-down menus, pop-ups, and other effects that play when specified conditions occur. For example, when there was a click on the plus sign or when the cursor went out of the window.
  4. Interaction with HTML elements on the page - A typical example of such an implementation is a landing page builder. The blocks are dragged with the mouse; by clicking on the left/right button, the font, colors and other parameters are changed.
  5. Graphic effects, animation - This includes moving objects like snowflakes or a countdown timer. We are also talking about smooth scrolling of the page, the appearance and hiding of objects, for example, when activating the slider in the "carousel" mode.

All of these types of operations are easy to spot on one landing page. This indicates the relevance of the jаvascript language. Moreover, in the site building market, various designers are more and more approved - from visual editors for CMS to independent platforms, where you cannot do without JS scripts.

How JS code works on the site

The user, by any action on the site, triggers an event, be it scrolling a page, clicking on a menu item or moving the cursor “inside the screen”. This is the basis for the use of scripts, which are easily "nested" into each other, if some events imply a different reaction of the browser.

How JS code works

The sequence of the JS scripts:

  • The user took some action.
  • The browser has registered the coincidence of certain conditions.
  • The jаvascript code "bound" to the event started running.
  • The page has been refreshed in whole or in part.

That's it, the script stopped working until the action was repeated or another module was activated. Reacting to an event becomes possible if the programmer has entered the JS script code into the site (page) template and placed a link to it in the right place (onclick command). If you don't, nothing will happen. The same forms of capturing contacts will become "ordinary pictures".

What jаvascript can't do in a browser

Despite its versatility, JS is not capable of replacing other languages. And all this is due to the desire of developers to increase security, as well as prevent unauthorized access to personal and commercial information. Such moments have to be taken into account by the coder so that the created resource does not become a "collection" of errors.

Examples of restrictions:

  1. Read, write, copy, run arbitrary files on the local storage. It is possible to allow the upload of certain types of files to the server, but not vice versa. In the case of downloading, they usually do without JS scripts.
  2. All windows and tabs within even one page are isolated from each other. When you open an additional form directly from the "primary", you will have to write a separate code so that they exchange the entered data with each other.
  3. Once launched, scripts interact only with the server from which the page was opened. It is allowed to work with third-party sites and domains, but this will require explicit permission.

The listed restrictions are aimed at reducing the risk of launching malicious code, including downloaded from the "left" address. It should be borne in mind that they only act on the browser (user) side. When executing code on the server, JS scripts have significantly more rights. To compensate for this difference, special extensions are installed on browsers.


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